This invention relates to an apparatus and method for grinding the teeth of a shaving cutter used to shave the surface of teeth of a gear workpiece such as a gear used in the transmission of an automotive vehicle. More particularly, the invention relates to the aforesaid apparatus and method in which the teeth of a shaving cutter worn due to repeated cutting of gear workpieces are reground to make it possible to cut gear workpieces again in excellent fashion.
When shaving the surfaces of teeth of a gear workpiece such as the gears of an automotive transmission, a shaving cutter is used, as disclosed in the specification of Japanese Patent Application
Laid-Open (KOKAI) No. 61-131819, by way of example. In the arrangement disclosed, a sliding base on which a gear workpiece is placed is provided so as to be movable back and forth with respect to the position at which the shaving cutter is disposed. As the sliding base is moved back and forth, the gear workpiece is meshed with the shaving cutte to shave the surfaces of the gear workpiece teeth.
In order to prevent a decline in the tooth surface cutting precision due to thermal deformation of the shaving cutter and a change in ambient temperature, thewell-known art mentioned above teaches to measure the tooth surface shape of the gear workpiece after shaving and obtain a deviation between the actually measured value and a proper value. The amount of movement of the sliding base is successively revised in accordance with the deviation value thus obtained, thereby maintaining a high cutting precision.
A the shaving cutter repeatedly shaves gear workpieces in the manner described above, the surfaces of the cutter teeth sustain wear. When this occurs, the tooth surfaces are subjected to regrinding so that the cutter can be used a number of times (e.g. scores of times). Thus, the effective service life of the shaving cutter is extended so that the cutter can be used over a long period of time before being discarded. This serves to improve production efficiency.
A problem encountered in the foregoing is that when the shaving cutter is reground a large number of times, the thickness of the teeth gradually diminishes with each regrinding. As a result, when a gear workpiece is cut by a shaving cutter which has been repeatedly reground, there is a change in the meshing state between the gear workpiece and the shaving cutter, such as a change in the meshing pressure angle. Consequently, in order to obtain the proper shape of the gear workpiece tooth surfaces, it is necessary that the shaving cutter tooth profile be sharpened by gradually changing the tooth shape little by little in dependence upon the reduced tooth thickness.
Thus, gear workpieces can be cut in substantially proper fashion when the shaving cutter is in good condition, namely when it is free of wear. However, when the shaving cutter sustains wear, a regrinding operation that relies upon a worker becomes necessary and demands that the worker have a high level of experience and skill. Thus, in the prior art, the regrinding of a shaving cutter is a difficult operation requiring an extended period of time and the precision with which the shaving cutter is ground (namely the precision with which gear workpieces can be cut) cannot be maintained at the desired value.